1.1 ,This specification covers vapor retarders for thermal insulation, specifically, flexible materials with permeance of 0.10 perm or lower and surface burning characteristics of 25 flame spread/50 smoke or lower. These materials are intended for use at surface temperatures of ,−,20 to 150°,F (−,29 to 66°,C). It does not cover mastics or barrier coatings applied in liquid form, nor materials intended for use as weather barriers.